The art of marine anchors has progressed to the point where one-sided designs are accepted as superior configurations in the interest of a balance of performance and strength. Anchors of this configuration termed asymmetrical anchors typically have a single fluke with one side of the fluke intended to meet the soil of the seabed. Such anchors have proven to be more efficient than symmetrical designs by way of both setting into the seabed more reliably, and generating a higher resistance for holding on a weight-for-weight basis, whilst being better suited for a construction that is strong and durable. It is also the case that the largest portion of demand is for drag embedment anchors, which are the usual choice for temporary anchoring as opposed to permanent mooring. Because of their nature, asymmetrical drag embedment anchors must necessarily orient themselves, after being dropped onto the seabed, into the correct attitude for which they are designed to set into the seabed in response to a pull on the anchor rode by the anchoring vessel. If this self-orientation does not occur, the anchor may in some circumstances rest on its back or its side and never present its fluke to the seabed. In such cases the anchor fails in its purpose. This self-orientation must be reliable, work across a large range of seabeds, and must also work if the anchor is pulled out of the seabed by way of a reversal or veer of the direction of pull on the anchor rode. Should this occur the anchor is expected to re-set itself without manual intervention. The two main methods of ensuring this self-orientation hitherto have principally been the attachment of a roll-bar to the rear of the fluke or the adding of weight ballast to the tip of the anchor. Other attempts have been made by shifting the position of the shank on the fluke and adding complex protrusions such as fins above the working surface of the rear of the fluke. Such constructions have inherent failings or disadvantages.
The shank of the anchor forms a lever which is subjected to forces applied from the rode attachment point and is therefore vulnerable to deformation or bending at or around the base if the fluke of the anchor is held firmly. This lever is necessary for temporary drag embedment anchors because the fluke must be able be aligned correctly by the rode's pull alone. High forces in normal usage will subject the shank to linear pulls. The highest forces are likely to be when the anchor is being retrieved, and is very well set and buried, or is fouled (stuck) on some obstacle. In this case the vessel may exert extremely high forces in an upward direction on the shank. A problem with existing anchors is that the shank is formed from a variant of either a flat plate with substantially even thickness or a simple I-beam. The former lacks strength on a weight-for-weight basis and the latter restricts burying performance of the anchor. This is clearly disadvantageous.
Also the anchor fluke is vulnerable to bending or deformation in two principle locations: firstly where the shank is mounted and forces from the rode are thereby transmitted, and secondly at the tip which is the first to encounter the seabed and may be subjected to hard rock or other underwater obstacles. This also is disadvantageous.
Another problem relates to performance as measured by setting effectiveness and ultimate holding capacity. The anchor shank and fluke may be constrained by geometry enforced by plate construction methods that result in a sub-optimal fluke surface area or higher mass than desirable. In turn this means a less efficient anchor on a weight-for-weight basis. This is disadvantageous to anchoring performance.
Existing anchors that self-right without the use of a roll-bar may make use of fins, modified skids, or other protrusions raised above the fluke surface. These protrusions collect soil from the seabed substrate in which the anchor is used, which may be compacted by the pressure of normal anchoring activity. This can alter the anchor's weight balance to the point it does not self-right as designed if the anchor is later pulled free from the seabed. Without self-righting the anchor cannot be relied upon to re-set. This is clearly disadvantageous.
Other anchors that self-right without the use of a roll-bar may make use of protrusions again extending from the rear or side of the fluke which are intended to interact dynamically with the seabed as the anchor is dragged, providing a rolling moment by way of deflecting soil. These designs do not self-right when the anchor is static but depend upon the proper combination of drag speed and ideal seabed conditions, which is clearly disadvantageous as such a combination may not be counted upon.
Additionally existing anchors that self-right without the use of a roll-bar make use of either a large amount of dead weight as ballast or place the shank impractically far forward on the fluke. The former makes the anchor less efficient on a weight-for-weight basis, and the latter causes both bow-roller compatibility problems and leaves the majority of the fluke unreinforced and subject to damage. These constructions are both disadvantageous.
Existing anchors that self-right by way of a roll-bar have hitherto made use of solid round bar or hollow tube. Solid bar is either too thin to reliably keep the rear of the anchor when upside-down from sinking into a soft seabed, or unnecessarily heavy if made of larger bar diameter. Alternatively a hollow tube may fill with mud entering by way of the openings which cannot be sealed if the anchor is to be hot dip galvanized. Neither method provides any further benefit once the roll-bar has performed its function of orienting the anchor to the correct attitude for setting. This is disadvantageous.
Furthermore anchors may sink some distance into the seabed when the rear edge of the fluke digs into the seabed. This reduces the ability of the anchor to roll into the correct attitude for effective use. Again this is disadvantageous.